I would like more references in the Concrete 02 material behaviour, I am having a hard time to define how the unloading and the reloading are defined in the hysteresis. Are there any references in this matter?
Mohd Hisham Mohd Yassin, "Nonlinear Analysis of Prestressed Concrete Structures under Monotonic and Cycling Loads", PhD dissertation, University of California, Berkeley, 1994.